Recent developments in the automotive market show an increasing demand for the use of electric motors within an automotive vehicle (car or truck, etc.). In particular, the electrification of a vehicle drive train requires powerful electric motors of typically, 20 kW to over 100 kW power. Present day hybrid-electric car concepts often even use 2 E-motors within the hybrid drive train.
These electric motors are normally driven by a 3-phase AC current which is provided from the DC bordnet through an inverter circuit. Therefore, these applications normally need a power control unit which controls and manages the electric power flow from the inverter to the E-motor. Thus, electric energy needs to be converted into mechanical energy and vice-versa. State-of-the-art hybrid systems therefore consist of an E-motor and a separate electronic box comprising the power management unit.
FIGS. 1, 2 and 3 show a typical example of such a state-of-the-art concept. A power control unit 10 with an inverter circuit 11 in a separate box or housing 12 (FIGS. 1 and 3) provides, via massive cables 13 (FIG. 1), the current connection to the E-motor 14.
One key element of the power control unit 10 is the DC/AC-inverter circuit 11. The main task of the inverter 11 is to transfer the DC-current/voltage into an AC-current/voltage and vice-versa. Converting DC- into AC-current is required in order to drive a motor powered by the DC-bordnet. This mode is also called “motor-mode” since the E-motor is used to drive the car.
Besides this “motor-mode” the E-motor can also be operated as a generator when mechanical energy from the car movement or from the combustion engine (not shown) is used to drive the E-motor 14. In that case mechanical energy is converted into electrical energy in order to charge the battery or to power the bordnet. In this “generator-mode” the inverter needs to convert AC-current generated by the motor into a DC current.
FIG. 1 shows a typical power control unit 10 driving E-motor 14. The top cover of the box 12 is removed to show inverter section 11. The inverter is formed in one or more modules 11 which are provided with output electric connections 13 between power modules, capacitors 20 (FIG. 2) and external connectors.
Not shown are the main circuit board and EMI screen which are on top of the power stage inside of the box 12.
FIG. 3 shows the closed power control box 12 of FIG. 1. FIG. 2 shows the heatsink 21 and the inverter modules 12 mounted on top thereof.
The inverter units 11 are mounted in the relatively big and heavy box or housing 12 forming the power control or management unit. Normally a main control board (not shown) is placed inside of this box 12 which includes among other circuits, the driver-ICs for the inverter, a microcontroller, software, protection and sensor analyzing circuits, and communication and I/O interfaces for communication with the board computer or the combustion engine control unit. The box 12 with the power control unit can also include further elements like a DC/DC converter for providing various voltage levels for the bordnet and other electronic systems.
Typical elements of such a power control unit according to the state-of-the-art are:
1 to 3 power modules (e.g. MOSFETs or IGBTs in a half-, H- or full-bridge configuration) for the inverter 11 which normally has to handle currents of several hundred amperes.
A heatsink 21 which normally needs to be actively cooled by a fluid coolant applied to inlet and outlet conduits to deal with the power losses of the inverter 11.
A connector frame providing the mounting space for (high) power connections (between E-motor phases and inverter) and the signal connections (between power control unit and the bordnet systems).
High current connectors or other assembly elements mounted to the connector frame for the wiring of the inverter to the E-motor.
Low power signal connectors for interfacing with the bordnet.
A box-cover.
The power control unit 10 is a separate box 12 which is placed in suitable locations of a car (e.g. in the trunk, under the passenger seat, in the engine compartment, or elsewhere) and is connected by cables or thick wires 13 to the E-motor 14 and other components of the drive drain.
The disadvantage of this arrangement is that long high current and, normally, high voltage cables 13 have to be provided between the E-motor 14 and power control unit 10. This incurs high costs. The required high-voltage connections such as cables, plugs and the like, are also a source of high power losses within the cables. The weight and the space requirements of the thick cables is also disadvantageous. Long cables are further disadvantageous for the EMI-requirements of the car due to the generation of electric noise and due to the inductance that they introduce into the electric circuitry of the power management system.
Further, the inverter power modules inside of the box 12 need protection against environmental conditions like dust, water, chemicals, and the like. The disadvantages of this are:
High cost added by the mechanical components like heatsink, connector frame, tight cover. The need for a connector frame with connectors is required by the physical separation of the inverter 11 and the E-motor.
The relatively large space requirements due to the box 12 itself.
Space requirements for placing the power unit within the car.
Another disadvantage of the present assembly is that the sensitive main control board (carrying a microcontroller, ICs and other elements) which cannot withstand high temperatures is close to the high power inverter 11 which produces considerable heat inside of the box 10. While the power switches of the inverter (MOSFETs, IGBTs or the like) normally can work at junction-temperatures of up to 175° C. these sensitive main board components are typically rated only up to 125° C. Therefore, additional means for thermal management of the power stage and main board within the box is needed, adding further costs, weight, space, and thermal burdens.
Besides thermal protection, the main board also needs to be protected from the electric field and noise generated when switching high currents in the power stage of the inverter 11. This EMI noise can disturb the sensitive functions of the main board. Thus, additional EMI protection is required for the main board in box 12. Thus, the main board is normally covered with a metal screening plate located between main board and power stage of the inverter to damp or screen the electric fields.